The field of the invention is sodium bicarbonate production and the present invention is particularly concerned with the preparation of sodium bicarbonate and hydrogen chloride by reacting an aqueous sodium chloride solution with carbon dioxide under pressure in the presence of an amine and an organic solvent.
The state-of-the-art of sodium bicarbonate production may be ascertained by reference to Israeli Pat. No. 33,552, U.S. Pat. No. 3,443,889 and the Kirk-Othmer, "Encyclopedia of Chemical Technology", Second Edition, Vol. 1 (1963), page 734 and Vol. 18 (1969), page 467, the disclosures of which are incorporated herein.
Assignee's U.S. Pat. No. 4,115,530 is incorporated herein to amplify one of the process steps used in the present invention.
A major part of the world sodium carbonate production takes place by calcining sodium bicarbonate in the Solvay process as the by-product given by the following formula: EQU NaCl+CO.sub.2 +H.sub.2 O+NH.sub.3 .fwdarw.NaHCO.sub.3 +NH.sub.4 Cl
The ammonia is recovered from the ammonium chloride usually by treatment with burnt lime according to the equation: EQU 2 NH.sub.4 Cl+CaO.fwdarw.2 NH.sub.3 +CaCl.sub.3 +H.sub.2 O
Large amounts of calcium chloride accumulate in the process, which together with the untreated sodium chloride are discharged as waste into the sewer system. The drawback of the Solvay process therefore in essence is that all of the chlorine of the converted sodium chloride is lost in the form of worthless calcium chloride, and furthermore the reacted sodium chloride is lost.
Again, in a way similar to the Solvay process, the chlorine which is used in the method of U.S. Pat. No. 3,443,889 is lost. U.S. Pat. No. 3,443,889 includes the procedure of preparing alkali carbonates from alkali chlorides and carboxylic acid in the presence of a strongly basic amine dissolved in an organic solvent. Only the amine is extracted from the particular aminohydrochloride formed, by treating the organic phase with an alkalinically active reagent for the purpose of feedback into the process.
It is known from Israeli Pat. No. 33 552 to prepare sodium bicarbonate and hydrogen chloride in a variation of the Solvay process where first a heterogeneous mixture of an amine dissolved in a polar organic solvent and a sodium chloride brine is treated with carbon dioxide under pressures up to 9 atmospheres, in the gaseous phase. The sodium bicarbonate is precipitated from the aqueous solution, the aminohydrochloride produced remains dissolved in the organic phase and is separated. Thereupon the amine is regenerated out of its hydrochloride by treatment with aqueous magnesium hydroxide and the aqueous magnesium chloride obtained is decomposed at temperatures up to about 500.degree. C. with the formation of magnesium oxide, magnesium oxichloride and hydrogen chloride. However, the hydrogen chloride produced is not necessarily water-free, depending on the process conditions so that it can be used commercially only in a restricted manner. This method suffers from another drawback due to the temperatures required for the production of hydrogen chloride and the related increased danger of corrosion and furthermore the additional use of magnesium salts.